The western national parks have operational mandates to specifically limit the human footprint. The sites are small and close together specifically for that reason. Dispersed camping is prohibited.
The private parks have to deal with the fact that most of the land in the area is public land, generally forest service and cannot be bought at any price. That makes the remaining private land extremely expensive. The private land is often very mountainous, since that is the attraction to the area and construction costs are vastly greater than constructing sites on a field in Nebraska. Seasons are short. Glacier's season is generally considered to run from late June thru September. Putting in as many paying customers as possible during that timeframe is a requirement to stay in business.